Today, robots have been widely used in various industries. When robots enter into our daily life, special attention must be paid to safety issues related to physical interaction between human and robots. Especially in robotic surgery, where interactions such as physical contacts between surgeons and surgical robots are inevitable, the safety requirements are much stricter. Flexibility or compliance at the joints of the robot can reduce the force acting on human body during collision or contact.
There are mainly two kinds of approaches to produce compliance in a robotic system: (1) active approach, where the compliance is produced from an action of control system rather than from a mechanical structure and (2) passive approach, where the compliance is produced from the mechanical structure rather than the control system. The active compliant approach has high programming ability and precise position accuracy, but it suffers from limitations such as delayed contact response, low reliability, high costs and complex control algorithms. Moreover, the safety cannot be guaranteed when sensors fail to work properly. A passive compliant approach often provides faster and more reliable response to dynamic collision than an active approach. However, a passive compliant system usually has a complex mechanical structure.
US Patent documents U.S. Pat. Nos. 924,749 and 6,666,283 disclose a cam based transmission mechanism that can open when high torque load acting on the coupling. However, the transmission mechanisms have only one effective working direction and only one working state, which is always flexible. US Patent documents U.S. Pat. Nos. 1,443,026 and 6,012,985 disclose another cam based transmission mechanism which have two working states: a rigid one and a free one, and also can work on both directions. However, the mechanism is too complex to implement in compact design. US Patent documents U.S. Pat. No. 8,021,071 and 8,235,827 disclose compliant joint designs for preventing an injury to a human by collision with robot. The designs have multiple working states and are simple enough for real application. However, these designs can only be used in the situation that power plant (motor), compliant joint and working device or end effectors are connected in serial, which leads the result of big volume and makes it difficult in real application.
Therefore, there is a need to provide a compliant safe joint which has small volume and multiple working states, integrates passive and active approaches and hence offers high operational accuracy, reliable intrinsic safety and high bandwidth to the impacts.